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首页> 外文期刊>Journal of Inorganic Biochemistry: An Interdisciplinary Journal >Inhibitory effects of nitrite on the reactions of bovine carbonic anhydrase II with CO2 and bicarbonate consistent with zinc-bound nitrite
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Inhibitory effects of nitrite on the reactions of bovine carbonic anhydrase II with CO2 and bicarbonate consistent with zinc-bound nitrite

机译：亚硝酸盐对牛碳酸酐酶II与二氧化碳和碳酸氢根与锌结合亚硝酸盐一致的反应的抑制作用

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Carbonic anhydrase (CA) is a zinc enzyme that catalyzes hydration of carbon dioxide (CO2) and dehydration of bicarbonate in red blood cells, thus facilitating CO2 transport and excretion. Bovine CA II may also react with nitrite to generate nitric oxide, although nitrite is a known inhibitor of the CO2 hydration reaction. To address the potential in vivo interference of these reactions and the nature of nitrite binding to the enzyme, we here investigate the inhibitory effect of 10-30 mM nitrite on Michaelis-Menten kinetics of CO2 hydration and bicarbonate dehydration by stopped-flow spectroscopy. Our data show that nitrite significantly affects the apparent dissociation constant Km for CO2 (11 mM) and bicarbonate (221 mM), and the turnover number kat for the CO2 hydration (1.467 x 10(6) s(-1)) but not for the bicarbonate dehydration (7.927 x 10(5) s(-1)). These effects demonstrate mixed and competitive inhibition for the reaction with CO2 and bicarbonate, respectively, and are consistent with nitrite binding to the active site zinc. The high apparent dissociation constant found here for CO2, bicarbonate and nitrite (16-120 mM) are all overall consistent with published data and reveal a large capacity of free enzyme available for binding each of the three substrates at their in vivo levels, with little or no significant interference among reactions. The low affinity of the enzyme for nitrite suggests that the in vivo interaction between red blood cell CA II and nitrite requires compartmentalization at the anion exchanger protein of the red cell membrane to be physiologically relevant. (C) 2015 Elsevier Inc. All rights reserved.
机译：碳酸酐酶（CA）是一种锌酶，可催化红细胞中二氧化碳（CO2）的水合和碳酸氢盐的脱水，从而促进CO2的运输和排泄。牛CA II也可能与亚硝酸盐反应生成一氧化氮，尽管亚硝酸盐是CO2水合反应的已知抑制剂。为了解决这些反应在体内的潜在干扰以及亚硝酸盐与酶结合的性质，我们在这里研究了10-30 mM亚硝酸盐对CO2水合和碳酸氢盐脱水的Michaelis-Menten动力学的抑制作用（通过停止流光谱法）。我们的数据表明，亚硝酸盐显着影响CO2（11 mM）和碳酸氢根（221 mM）的表观解离常数Km，以及CO2水合的周转数kat（1.467 x 10（6）s（-1）），而对碳酸氢盐脱水（7.927 x 10（5）s（-1））。这些效果分别证明了与CO2和碳酸氢盐反应的混合和竞争性抑制作用，并且与亚硝酸盐与活性位点锌的结合一致。此处发现的对CO2，碳酸氢盐和亚硝酸盐的高表观解离常数（16-120 mM）总体上与已公开的数据一致，并且揭示了可用于结合三种底物在体内水平的游离酶的大容量，几乎没有或反应之间无明显干扰。该酶对亚硝酸盐的低亲和力表明，红细胞CA II与亚硝酸盐之间的体内相互作用需要在红细胞膜的阴离子交换蛋白上进行区隔，以实现生理相关性。 （C）2015 Elsevier Inc.保留所有权利。

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